Fire-detecting wire.



C. A.*HARSCH.

FIRE neecmc WIRE.

APPLICATION FILED JULY 21.1917.

1,278,920. Patented Sept. 17, 1918.

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UNITED STATES PATENT OFFICE.

CHARLES AUGUST HARSCH, OF NEW YORK, N. Y., ASSIGNOR, BY MESNE ASSIGNMENTS, TO MOUNT FIRE ALARM CORPORATION, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

FIRE-DETECTING WIRE- Specification of Letters Patent.

Patented Sept. 17, 1918.

Application filed .Tuly 27, 1917. Serial No. 183,138.

To all whom imag concern.'

Be it known that I, CHARLES AUGUST Hanson, a citizen of the United States, residing in the city of New York, borough and county of the Bronx, State of New York, have made certain new and useful Improvements in Fire-Detecting Vires, of which the following is a specification` This invention relates to a fire detecting wire or conductor and the object is to provide such a wire or conductor that is economical in cost of material and construction, adapted to be easily handled and folded or bent without injury or damage in transportation and installation and which may be adapted to initiate an alarm at any desired temperature within a wide range; that is, from a point as low as 100 degrees Fahrenheit.

The improved wire consists of a central core or alloy of easily fusible metal in tape or ribbon form, such an alloy usually including cadmium, bismuth, lead and tin. This alloy is preferably rolled; it is preferred to employ a strip one eighth of an inch in width and, say, two one hundredths of an inch thick; this alloy strip is placed between a ribbon of steel and a ribbon of copper; these ribbons are preferably the same width and one-half the thickness of the alloy core and are arranged parallel upon opposite sides of the alloy core. Steel and copper are employed because they have different coefficients of expansion under the effect of heat and when the alloy core expands and fuses the two metal strips tend to separate slightly, straining and sometimes rupturing the insulation (to be described), at the edge or edges of the strips, the fusible alloy escaping, expanding, and projecting between the edges of the strips on one or both sides. An insulating coating is applied to these strips after they are laid closely parallel, and all three in electrical contact, so that when the alloy is heated itis forced outward and perforates the insulating coating, making electrical contact with the armor. This armor is applied cold and it is preferred to use a helically disposed steel tape, the edges of the convolutions making close contact.

The accompanying dra wings illustrate the invention. The fusible tape or ribbon a., is preferably composed of cadmium, bismuth, tin and lead in proportions well known and adapted to fuse at a temperature as low as may be desired; it may be as low as 100 degrees Fahrenheit. A strip or ribbon of copper b, and a strip or ribbon of steel c, are located parallel, upon Opposite sides of the intermediate, fusible strip a.. A complete coating of insulating material envelops the three elemental parts a, b, and c, preferably consisting of some distillate of petroleum, like ozokerite or it may be a woven fabric, of coarse weave, saturated with ozokerite; bitumen is sometimes successfully employed or a comparatively soft vitreous enamel may be employed as a coating. Outside the insulating coating, whatever the specific character of the coating employed, is a helical winding of steel tape, say five thirty seconds of an inch wide, and thin enough to permit of flexing or bending, say, one one hundredth of an inch, so that the structure may be reeled or wound in transportation and may be caused to turn a corner without injury when disposed upon the wall.

When heat is applied from a tongue of Haine, such as is due to an ignited match, the steel winding 71 freely conducts the heat, as does the tape b, and the tape c, so that the fusible ribbon a, is immediately softened and expands, the two tapes Z9 and c slightly separate, expanding in opposite directions, tending to free the alloy core and also rupture the insulating coating, thus contributing to the flow of the fused alloy and promote the sidewise movement of the fused alloy. The fused metal a, projects, in needle form, penetrating the insulating coating c, and electrically connecting the direct member of the conductor composed of the elemental parts a, b, and c, with the return conductor it; this closes a normally open circuit and a signal or alarm results, in the well known manner.

Vhat I claim is:

l. In a fire detecting wire the combination of a central tape or ribbon composed of an easily fusible metal, two metal tapes, one on each side of said fusible conductor, a layer of insulating material enveloping said tapes or ribbons and an exterior conductor maintained in position in contact with said insulating coating.

2. In a fire detecting wire the combination of a central tape or ribbon conductor composed of an easily fusible alloy, two metal tapes one on each side of said fusible conductor and electrically connected with the fusible conductor and each other, alayer of sides thereof in mechanical and electrical insulating material enveloping said ribbons contact therewith, a coating of insulating and an exterior conductor in close proximity material and a conductor in mechanical enl0 mechanically united therewith. gagernent with said insulating coating upon 5 3. In a re detecting Wire the combination the outside thereof.

of a central tape or ribbon of fusible metal @copper tape and e steel tape upon opposite CHARLES AUGUST HARSCH.

Copies of this patent may be obtained for ve cents each, by addressing .the Commissioner of Patents, Washington, D. C. 

